Playing or fighting? Home cage dynamics in crowding or social instability paradigms contribute to stress and reproductive impairments in adult female Wistar rats (2025)

Poitras, M., Ouellette, É. A., Pellis, S. M. et al.

Abstract

Play fighting represents a key behavioral component in group-housed rats, yet its contribution to the outcomes of social stress paradigms remains unassessed. This study characterized play fighting behaviors over time in two social stress conditions involving crowding. We also evaluated whether play style was associated with changes in stress and reproductive signalling. Methodology 56 adult female Wistar rats were exposed to 21 days of high density housing (HDH; 8/cage, stable groups) or social instability (SIS; alternating days of isolation and HDH, unstable groups). Home-cage behaviors and corticosterone were determined at discrete timepoints throughout the protocol exposure. Rats (12/stress group) were categorized as high (HP) or low (LP) players to examine how play profiles influenced stress response and reproductive impairments. Results In both groups, player profiles remained stable throughout the housing period. SIS rats performed more nape contacts and pins than HDH rats, but showed shorter pin length. HP-SIS rats had significantly heavier adrenal glands than LP-SIS rats and HP-HDH rats, and spent more days in estrus compared to HP-HDH. Corticosterone secretion profiles were differentiated by an immediate rise in HDH rats compared to delayed increase observed in the SIS group, although player types showed no further associations. Conclusions In unstable social environments such as SIS, short, frequent pins may reflect recurrent attempts to establish social hierarchies, with high-playing SIS rats showing increased adrenal weights relative to low-playing and HDH counterparts. These findings support the hypothesis that play behaviors serve distinct purposes depending on the social context.